In the case of spark ignition engines with direct injection of the fuel into the combustion chamber, it is necessary to rapidly obtain well controlled spraying of the fuel jet. Specifically, the spraying must exhibit a certain directionality and a penetration rate sufficient to obtain a fuel-air ratio around the spark plug at the moment of ignition that enables the mixture to be ignited. However, the depth of the sprayed jet which increases with the injection pressure, must not be excessive so as, in particular, not to spray fuel against the walls of the combustion chamber.
To this end, use has been made of swirl injectors in which the fuel is guided with a swirling motion in the injector before being sprayed. These injectors make it possible to obtain good atomization but, in addition to their high cost, they have the disadvantage of creating a high internal pressure drop in the supply pressure and consequently make it essential to apply a high force in order to actuate the control needle of these injectors. In practice, it is difficult to use these injectors with a fuel supply pressure above 150 bar. Moreover, these injectors create a poorly directional jet with a relatively low rate of penetration into the chamber, which makes it more difficult in some cases to obtain a stratified mixture, that is to say a gas mixture whose fuel-air ratio is greater in certain defined parts of the combustion chamber.
In the case of these engines, it is also known practice to use multihole injectors comprising a plurality of orifices which spray fuel jets in divergent directions. These injectors make it possible to obtain a higher penetration rate and very good directionality of all the fuel jets. Moreover, they create fewer internal pressure drops and are less difficult to manufacture than injectors provided with a swirl atomizer. On the other hand, the fuel is sprayed with less efficiency since the contact area with the gases is smaller and the fuel jet is less turbulent than with the swirl injectors. Consequently, the degree of mixing of the fuel with the combustion chamber gases is less able to be controlled in certain situations, which has harmful consequences in terms of the engine efficiency and the emission of pollutants.
An object of the present invention is to overcome these disadvantages by providing an injector which allows high pressure direct injection into the combustion chamber with high efficiency spraying and a certain directionality, without however consequently increasing the depth of penetration of the atomized fuel jet and the cost of the injector.